a) Field of the Present Invention
The invention is directed to a method and an assigned device for decentralized transmission of data on a transmission line corresponding to the preamble of the independent claims.
b) Background Prior Art
Transmission lines and diverse types of data transmission via such lines are generally known. Recently, optical transmission lines have become increasingly important for various reasons. In addition to the optical point-to-point connections, there are also complicated network structures with optical lines. For example, in an article entitled "Optical fibres in local area networks", Communications/Communications International, October 1985, pages 19 ff., B. Viklund describes various network structures with glass fiber cables for distribution networks and for networks with connections between different subscribers which can be set up individually. In the latter, a ring configuration is most favorable. The subscriber stations of an optical transmission line of the aforementioned type are connected to the respective utilized fibers via optical couplers.
At present, there are couplers, switches and modulators based on GaAs semiconductor material for optical systems which utilize electro-optical effects for influencing light. These elements work up to frequencies in the gigahertz range.
The use of address-coded packets for transmitting data is generally known. Such packets comprise a head part (header) and a data part, wherein the head part contains all necessary data for the respective packet and the participating transmission devices, particularly the respective transmitter and receiver. The data part is available for the data to be transmitted. If it is empty, it is referred to as an empty packet.
Various methods are known for producing address-coded packets and converting empty packets into data packets. In this respect, reference is made e.g. to the patent CH 550 521 which describes one of the first methods presently known as "buffer insertion". What all of these methods have in common is that they have a delay at some point, be it a matter of the insertion of a new packet into an existing stream of packets, wherein the entire stream is delayed by the length of a packet, or be it a matter of having to wait for the reading of the head part of a packet before it is clear whether or not it is an empty packet, etc.
In optical systems, a controlled delay on the transmission lines was (until now) not possible. Such a delay can only be effected in that it is effected in the electronic part of the system, e.g. by means of a shift register. In an optical transmission line chiefly comprising so-called passive subscriber nodes which have no active light source (e.g. a laser diode), there is the problem of providing a method for detecting passing empty packets entirely without delay and filling them with prepared data. These methods must be consistent with the method of receiving data packets which run or arrive via the same transmission line.
The solution to this problem is provided by means of the independent claims, while the dependent claim indicates a construction of the invention. Accordingly, it is now possible to set up relatively simple and accordingly inexpensive subscriber nodes in optical transmission lines.
The invention is explained in more detail in the following by way of example with the aid of seven diagrams.